Shaped product



Patented July 4, 1944 UNITE-o STATE William H.

smirnn rnonuc'r Markwood, In, Wilmington, DeL, as-

si nor to E. L du Pont de Nemours a Company, Wilmington, Del., acorporation of Delaware No Drawing. Application November 4, 1941,

Serial No. 417,807

13 Claims.

This invention relates to lustrous, opaque sheet material, especiallythin, flexible, synthetic polymer film. More particularly it appertainsto the treatment of continuous, transparent webs of polyhexamethyleneadipamide to engender a pearlescent efl'ect therein.

In U. S. A. Patents Nos. 2,071,251, 2,071,253, 2,130,523 and 2,130,948to Carothers there is described a new class of fiber-forming materialswhich are'now commonly referred. to as synthetic linear condensationpolymers. ing of such materials int thin, transparent, coherent,self-sustaining films is disclosed in several U. S. A. patents, forexample, Nos. 2,141,169 (Catlin), 2,212,770 (Foster), 2,212,772(Graves). and 2,216,735-6 (Carothers). The preparation of similar sheethaving a pearlescent appearance is a deslderatum, inter alia, because ofits great decorative value, The common methods of producing this efiect,for example, by incorporating pearl-essence, are not satisfactory forvarious reasons, including the expense of adding material and theweakening efi'ect of such material on the polymer.

The primary object of this invention was to produce decorative eflectsin'polyhexamethylene adipamide and similar synthetic linear polyamidesheet by inexpensive means. Other objects were to producepoiyhexamethylene adipamide and related nylon films with a highlyappealing lustrous pearlescent effect, to produce silverypolyhexamethylene adipamide films without incorporating extraneousmaterials therein, and to process ordinary transparent shapedpolyhexamethylene adipamide products, without chemical treatment, insuch a way that, although they do not, they appear to containpearl-essence. A general advance in the art, and other objects whichwill appear hereinafter, are also contemplated.

It has now been found that transparent sheets oi polyhexamethyleneadipamide and the like assume a pearlescent appearance when drawn undercertain critical conditions, principally moisture content. An increasein length of about 300% (the product being four times its originallength) results when-this drawing is in one direction. The pearlescenteffect is remarkably stable. Samples of the sheet soaked for over a weekin water are without any alteration in appearance, and samples stored inordinary atmospheres for over a year show no noticeable change. I

How the foregoing objects and related ends are accomplished will beapparent from the following exposition, in which are disclosed the prinThe shap-- ciple and divers, embodiments of the invention, including thebest mode contemplated for carrying out the same.

In carrying out the present invention, transparent polyhexamethyleneadipamid sheet containing a critical amount of moisture is drawn orstretched in one or more directions at such a rate that a pearlescenteifect develops therein. Such sheet tends to. become brittle when almostcompletely dry, and-it is therefore necessary that the drawing operationnot be carried out under conditions of extreme dryness. Sheet which hasbeen subjected to an atmosphere which is too humid can be dried in anyconventional or desired way.

For convenience, the moisture content is stated in terms of the relativehumidity of the circumambient atmosphere with which the sheet is inequilibrium. A relative humidity of 10% has been found to be a practicallower limit, and 30% a practical upper limit, for the atmosphere used tocondition or equalize the sheet before draw ing. Sheet conditioned atrelative humidities between 15% and 25% have been found to-give the mostsatisfactory results. These relative humidities are based'on ordinarynormal room temperature, i. e.. 20. C.

The proper limits (lower and upper) of relative humidity essential areinfluenced to some extent by the thickness of the sheet being treated,principally because of the time factor involved'in bringing the sheettoan equilibrium.

These limits need not be set forth specifically, since they are easilyand more satisfactorily determined empirically.

In one specific embodiment, a strip of polyhexamethylene adipamide washeld in such a way that a 3 inch length was subjected to stretching, andit was drawn at a rate which produced a pearlescent effect, in this caseVa of an inch of material having a pearlescent appearance being producedper second. This is near the minimum rate of drawing which can beemployed for this particular polymer. A drawing rate which produced 1.5inches of pearlescent effect sheet per second was found to result in toofrequent ylene diammonium sebacate, and the interpolymers ofhexamethylene diammonium adipate, hexamethylene diammonium sebacate andcaprolactam (d-amino-caproic acid) v The rate of drawing or speed ofconversion is a subsidiary consideration, but it does depend to someextent upon the composition being drawn, for example, a much more rapidrate is necessary for polyhexamethylene adipamide than forpolyhexamethylene sebacamide. To amplify, practically any rate ofdrawing, regardless of how slow, will produce the desired effect in thelatter product, but a very rapid rate is necessary for the former. Inall cases the maximum drawing rate is determined by sheet breakage.

The polyamides. generally speaking, comprise the reaction product of alinear polymer forming composition, for example, one consistingessentially of bi-functional reacting material which comprises insubstantial amount molecules containing two amide-forming groups, eachof which is complementary to an amide-forming group in other moleculesin said composition. They can be obtained, by example,- by self-poly-'merization of mono amino mono carboxylic acids or by reacting ,diamineswith dibasic carboxylic acids in substantially equimolecular amounts, itbeing understood that this reference to amino acids. diamines anddibasic carboxylic acids is intended to include the equivalentamideforming derivatives of these reactants or similar products. Theaverage number of carbon atoms separating the amide groups should be atleast 2.

Modification of the polymers with minor amounts of resins, for example,phenol formaldehyde resins, does not prevent the production of ofdrawing, to produce a sheet which a not qui opaque but which is onlytranslucent.

It is often convenient to process sheet according to this inventionshortly after its solidificationin melt casting processes such as thatde- .scribed in U. S. A. Patent No. 2,212,710. Such sheet need only beallowed to pick up the critical amount of moisture before being drawn.

The invention is not limited to the treatment of sheet material toproduce a metallic effect.

Such articles have been made the basis of the description mainly forconvenience. Other shaped products such as yarns, and mono articles likebristles, behave similarly when so treated, and give equal or betterresults. Regardless of the external shape of the product having thepearlescent effect, it contains elongated voids, the presence of whichcan be shown by microscopic examination, which are substantially uniformin size and shape.

An interesting and unexpected characteristic of the products of thisinvention is that they may be retransparentized by the application ofpressure. This property has numerous useful and ornamental applications,for example, the sheet may be stamped with decorative patterns orindicia of various kinds such as trade-marks, which are transparent as aresult of the pressure exerted by the die or stamp utilized. The opaquesheets of this invention may be written on by using a stylus or similarinstrument, thereby providing va permanent record which is obliteratedonly by the application of greater pressure or the pearlescent efiect.In many cases sheets containing 10% to 20% of resins such asp-tertiarybutyi phenol formaldehyde resins, are more susceptible to theproduction of the pearlescent effect than sheets without the resins (butotherwise identical).

Vinyl polymers which are capable of being cold drawn, for example,polyethylene, interpolymers of unsymmetrical dichlorethylene (with vinylchloride, vinyl acetate and the like), and to a lesser extent, theinterpolymers of polyvinyl chloride and polyvinyl acetate, behavesimilarly to the polyamides.

The products used in the practice of this invention are of highmolecular weight and generally oan be obtained with a crystallinestructure, as evidenced by X-ray powder diffraction patterns in themassive state. The high molecular weight required for the best-fiberforming properties is obtained by continuing the polymerization untilthe intrinsic viscosity (as defined in U. S. A. Patent No. 2,130,948 toCarothers) is at least 0.4. Such polymers can be cold drawn (that is,drawn under tension in the solid state) with permanent and high linearextension from 200% to 500% or more to yield textile fibers showing byX-ray examination molecular orientation along the flber axis. Referenceis made to the patents mentioned elsewhere in this specification forfurther details.

The mechanical features of the drawing operation can be varied asdesired, and the stretching procedures of this invention may bedescribed as cold drawing, as defined in U. S. A. Patent No. 2,130,948.

Although the invention has been described in terms of the production ofan opaque film, it is possible in most cases, by the control of the ratedeterioration of the sheet. As an example of such a use, the preparationof a bank check from such material may be mentioned. The writing on sucha check would be exceedingly difllcult to alter without detection.

The shaped products of the present invention may contain minor amountsof a material suchas pigments, delusterants, etc. The finished productsmay be dyed before or after braiding, weaving, and like operations, withacid and basic dyes and the so-called acetate colors. Amazinglybrilliant and highly pleasing products are obtained in this manner.Apparently the high reflectance due to the pearlescent efiect, combinedwith the color sensation arising from the dye, is in proper balance togive a most pleasing sensation.

Surprisingly, the products of this invention possess as good tenacity asproducts prepared from the same materials but drawn more slowly or in amanner which does not bring out the pearlescent effect.

Other advantages and uses of the invention will be obvious to thoseskilled in the art. It is infrequent that a valuable and highlydecorative material such as that described herein, can be produced bysuch an inexpensive process and without the added expense and weakeningeffect transparent film composed of a synthetic linear polyamide havinga moisture content in equilibrium with an atmosphere of 10%-30% relativehumidity, whereby to impart a to said film. 1

9. The process which comprises drawing a transparent film composed of asynthetic linear polyamide having a moisturecontent in equilibrium withan atmosphere of 10%-30% relative humidity, whereby to impart apearlescent eifect to said film, said polyamide comprising essentiallythe reaction product of a linearpplymeramide, said film having apearlescent eflect due to the presence therein 01 minute elongatedvoids, said polyamide comprising essentially the reaction product of alinear polymer-forming composition which comprises a substantial amountof reacting material selected from at least one of the groups consistingof (a) monoamino carboxylic acids and (b) mixtures of diamine withdibasic carboxylic acid.

5. A film composed of polyhexamethylene adipamide, said film having apearlescent eflect due to the presence therein of minute elongatedvoids.

,6. The processwhich comprises drawing a transparent shaped bodycomposed of a synthetic linear poiyamide having a moisture content inequilibrium. with an atmosphere of l0%-30% relative humidity, whereby toimpart a pearlescent and to said body.

7. The process which comprises drawing a transparent shaped bodycomposed of a synthetic linear poiyamide having a moisture content inequilibrium with an atmosphere of 10%-30% relative humidity. whereby toimpart a pearlescent eflect to said body, said polyamide comprisingessentially the reaction product of a linear polymer-forming compositionwhich comprises a' substantial amount of reacting material selected iromat least one of the groups consisting of (a) mono-amino carboxylic acidsand (in mixtures of diamine withdibasic carboxylic acid. 8. The processwhich comprises drawing a forming composition which comprises asubstantial amount of reacting material selected from at least one ofthe groups consisting of (a) mono-amino carboxylic acids and (b)mixtures of diamine with dibasic carboxylic acid.

10. The process which comprises drawing a transparent film ofpolyhexamethylen'e adipamide having a moisture content in equilibriumwith an atmosphere of 10%-30%- relative humidity, whereby to impart apearlescent effect to said film.

11. The process of claim 6 in which said polyamide has amoisture'content in equilibrium with an atmosphere of 15%-25 relativehumidity.

12. The process which comprises drawing a transparent shaped bodycomposed of a synthetic linear polyamide having a moisture content inequilibrium with an atmosphere of 10 %-30% relative humidity, wherebytoimpart a pearlescent eiiect to said body, and rendering sections of saidpearlescent body transparent by application or pressure.

13. The process which comprises drawing a transparent film composed of ssynthetic linear polyamidehaving a moisture content in equilibrium withan atmosphere of 10%-30% relative humidity, whereby to impart apearlescent eflect to said film, and rendering sections oi saidpearlescent film transparentby application of pressure.

WILLIAM H. MARKWOOD,

pearlescent eflect I

